The present invention relates to improvements in dryer drums for continuously drying a web of paper in a papermaking machine, and more particularly to an improved condensate removal structure.
In a papermaking machine a plurality of dryer drums are arranged in sequence for carrying a continuous web of paper in a serpentine fashion through the dryer section. The dryer drums are steam heated, and the drums are usually constructed of a cylindrical outer shell with a smooth outer surface for carrying the paper web with heads at the ends of the drum shell which are provided with supporting bearings for rotatably mounting the drum. Means are provided at the bearings for directing steam into the drum and as heat is transferred to the web supported on the surface of the shell, condensate tends to form which must be removed so that it will not have an insulating effect and reduce the heat transfer from the steam to the shell.
In a typical construction so that the heat transfer ability of the drum is increased, the shell is made as thin as possible, and for strength, a plurality of annular raised ribs are located on the inner surface of the shell with grooves therebetween. The condensate collects in these grooves, and it is imperative that it be effectively removed for increasing the efficiency of the dryer drum, and in high speed papermaking machines, it is imperative that heat transfer be maintained at maximum efficiency and that the insulating effect of condensate collected within the drum be maintained at a minimum and be immediately and effectively and uniformly removed.
In accordance with a provision of the present invention, there are provided a plurality of elongate tubes which suck the condensate from the base of the grooves and the tubes are uniquely constructed and supported for removal of the condensate.
In order to obtain good operation and a high coefficient of the transmission of heat to the paper web on the outer surface of the drum, it is advisable that the thickness of the condensates which accumulates in the bottom of the drum be maintained at a minimum, and it is also imperative that this thickness remain the same in all of the grooves to maintain the same coefficient of heat transmission over the whole length of the surface of the drum.
Presently known drums can be generally categorized in two types. One type has condensate collectors which are fixed to the inner surface of the shell, and the other type has condensate collectors which are fixed and supported to the central shaft of the drum. The first type insures the maintenance of the distance between the collector tubes within the drum and the bottom of the grooves, but has the disadvantage that with rotation of the drum, centrifugal forces generated by the mass of the collectors make the shell deform resiliently causing it to be polygonal because of the concentration of such forces at the location of the collectors.
Drums which have collectors that are supported on the central shaft have the disadvantage that there is no good control over the distance between the open ends of the collector tubes and the bottom of the grooves particularly because dimensions change with thermal deformation of the parts as temperatures change. There is thus a need for control over the depth or thickness of the condensate which rims at the bottom of the grooves. Another problem is encountered that small tubes cannot be mounted with a very small spacing between their open ends and the inner surfaces of the shell because contact can occur between the tubes and the bottom of the grooves in operation generating wear and stresses on the shell.
An object of the present invention is to provide a steam dryer drum and condensate removal structure which will avoid the aforementioned disadvantages.
A further object of the invention is to provide a condensate removal system utilizing individual tubes for the grooves wherein the tubes can be readily and accurately adjusted relative to the bottom of the groove for uniformity of spacing between the ends of the tubes and the groove.
A still further object of the invention is to provide a condensate removal system for a grooved or ribbed dryer drum wherein the radial spacing between the open receiving ends of condensate collector tubes and the bottom of the grooves remains constant independent of deformations of the shell during operation and independent of changes of dimensions due to thermal deformation.
In accordance with the principles of the invention, there is provided a rotary steam dryer drum for a continuous traveling web of paper wherein the drum is supplied with steam for drying the web and has a cylindrical shaped shell with a smooth outer surface and with heads at the end of the shell to support the drum in rotation. Within the shell on the inner surface are a plurality of ribs with circumferential grooves therebetween, and a plurality of axially extending collectors is supported and disposed within the interior of the drum to receive and take up the condensation resulting from the steam and to convey it out of the drum. The axially extending collectors are provided with a plurality of small elastically deflectable tubes which project in both circumferential directions from the collectors in such a way as to have the base end securely mounted on the collector for the flow of condensate from the tube to the collector and having the free end biased toward the bottom of the groove but provided with a lugged tube positioning element which rests on the inner surface of the ribs adjacent the grooves in order to maintain the free end a predetermined accurate controlled distance from the bottom of the groove.
Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings in which: